I guess we can assume that the ID was accurate, although there can be a big difference between typical "carpet" beetles and hide beetles, with respect to the things they eat. Both kinds are in the family Dermestidae, but hide beetles are more often associated with carcasses and the final bits of skin, flesh, and hair left on the carcass once the flies and other initial insects are through with it. Typical carpet beetles feed on the hair or feathers of carcasses as well as on any grain-based food materials, so old rodent baits, bags of baking goods, dry pet foods are all susceptible to infestation from these smaller, oval beetles. Carpet beetles also feed on dead insects and their assorted remains, so old bee hives or wasp nests often have carpet beetles in them feeding on leftover pupa and shed exoskeletons. Bird nests with leftover feathers or dead chicks could also be a food source for them.
Which leads us to the question of what might exist in or around this fireplace that could be offering either of these bugs the food they look for. Depending on what kind of fireplace and chimney are here there could be little voids or alcoves up inside that a chimney sweep's work might not touch, although with their spinning brushes a thorough job ought to dislodge old wasp nests or bird nests. Perhaps you can seal off the opening at the bottom of the fireplace and place some glue traps on either side of that cover, such as plastic sheeting. This may enable you to determine, from captured beetles, which side of the opening the bugs are coming from. The fireplace certainly is not needed in Nevada this time of year, so sealing it shut for awhile shouldn't be any heartache for the customer and it might help you to narrow the search. If all the beetles you find are on glue traps within the fireplace it could suggest that the problem must be somewhere up inside the chimney.
If the captured beetles are on the living area side of the fireplace then a continued search for the source is needed, and you might concentrate on looking for grain-based foods rather than animal fibers, although never rule out anything. The adult beetles, in particular, are very active, and may be found wandering well away from their origin as the larvae. I myself had an ongoing problem with them that we finally traced to cupboards in the laundry room where we kept dog "biscuits", and one of the large biscuits had fallen behind things for most of a year and supported a large population of the carpet beetles. But, there could be wool blankets in storage, wool carpets nearby, wool tapestries on the wall, and other unusual sources near that area. I have also seen ongoing carpet beetle problems due to old rodent baits tossed in the attic and left there. You might investigate this possibility and ask the customer if they have done any rodent baiting themselves.
There are pheromone traps for carpet beetles and these can be placed here and there throughout the home, the attic, and even the crawl space. Inspecting the glue pads later may offer some clues as to where the beetles are most common and possibly coming from. I hate the idea of using only insecticides to resolve the problem if the source has not yet been found and dealt with. If you have a hidden source it will continue to pump out the adult beetles and continue to attract more of them to the area, since this is the role of these beetles - recycling leftover plant and animal materials. Contact insecticides are great for the mop-up operation to kill any wandering adults and larvae, and any of the pyrethroids should be excellent for this.
If you determine that somewhere up inside the chimney is the source this is a tough problem. Obviously accessing the exact source is impossible. You may be able to snake a camera up inside the chimney to take a look around, but rigging that up could be interesting. Perhaps another visit from the chimney sweep with more exact instructions on what to try to remove would help.
Mr. Pest Control
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